The present invention relates to an improvement in a driving mechanism including a series of wheels of an electric clock to operate a clock pointer intermittently with a step motor.
In a hitherto used electric clock provided with a step motor wherein the rotor was rotated by a definite angle in one direction at each driving pulse, a method was generally used in which a pointer such as a second hand is operated intermittently by connecting a series of gear wheels to a pinion directly connected with the rotor. In this method, however, since the movement of the rotor is transferred as it occurs, when the rotor moving in step at each pulse is stopped, a vibration produced by the inertia thereof will be transmitted to the second hand so that it is difficult to observe the second hand.
Consequently, some means have been considered to resolve such a defect. One is a means of loading a frictional piece to a series of gear wheels to which the second hand is directly connected, or to make a click piece operate. But, as an unnecessary load is applied by either of them, it is necessary to enlarge the output of the step motor, which brings about a decrease in battery life if a battery is used. In another means where the inertia of the rotor is reduced as the size of the rotor should be minimized as far as possible, the output torque of the motor will become small so that there arises a disadvantage in reduced reliability. And in order to increase this torque characteristic, a magnetic material of high energy content should be used, resulting in high cost. Therefore the main object this invention consists in eliminating these defects. And the secondary object is to provide a driving mechanism in which the gear train beyond the driven wheel is not connected when the rotor is about to start its rotation so that the rotor starts under a no-load condition so that the starting characteristic of the rotor can be improved. And in a hitherto-used electric clock, in case of correcting the time, it was formerly needed to provide a mechanism in order to prevent the second hand from moving together with the second wheel prevented from rotating, simultaneously with pushing of the time-correcting button. Therefore the futher object of this invention is to remove the the requirement for this mechanism.